1. Field of the Invention:
This invention relates to a scanning assembly for use in a flat-bed scanner, photocopier, facsimile machine, flat-bed output plotter or similar device. In particular, it relates to the imager (sensor and exposer) support and transport mechanisms of xe2x80x9cflat-bedxe2x80x9d type scanning devices.
2. Description of the Problem and Prior Art:
In a typical scanning device of the xe2x80x9cflat-bedxe2x80x9d configuration, a document to be scanned or exposed is placed face down on a platen window, while an imaging system on the opposite side of the platen window traverses the document, imaging the document through the window. While the problems described herein and the invention are applicable to input and output devices of the flat-bed type, including input scanners, photocopiers and output plotters, the discussion will be in terms of input scanners. It would be clear to one of ordinary skill in the art how to modify the invention to work for other flat-bed devices. The imaging system, typically an input scanner, is typically comprised of an illumination unit, focusing optics, and a linear imaging array. During scanning, a portion of the imaging system traverses the document in a direction perpendicular to the length of the linear imaging array. Existing imaging system configurations depend on many factors and typically use either charged coupled devices (CCD) or contact image sensors (CIS) imaging optics. In a typical prior art CCD-based scanner, some combination of the illumination unit and focusing optics traverses the document, while some combination of focusing optics and CCD array generally does not move. In a typical prior art CIS-based scanner, the illumination unit, fixed focusing optics and linear imaging array are contained in an integrated unit which traverses the document. This invention is applicable to the imaging system transport mechanism of CIS-based scanning devices although it also is applicable to other flat-bed imaging devices. Since the traverse mechanism used in CIS-based scanners have evolved from those designed for CCD-based scanners, it is appropriate to consider prior art CCD designs as also being prior art to the present invention.
In prior art systems, the traversing motion of the imaging system down the length of the scanner is usually accomplished by one of the following methods. The first prior art method includes a guide shaft of the length of the scanner and a drive mechanism. See for example U.S. Pat. No. 5,379,095 to Oishi entitled IMAGE READING APPARATUS WITH THE OPTICAL READING UNITS AND PHOTOELECTRIC CONVERSION DEVICE MOUNTED ON A COMMON GUIDE MEMBER (issued Jan. 3, 1995) and U.S. Pat. No. 5,610,731 to Itoh entitled IMAGE SCANNER HAVING CONTACT-TYPE IMAGE SENSOR MOVABLE UNDER AUTOMATIC DOCUMENT FEEDER (issued Mar. 11, 1997). In these prior art systems, the imaging system and shaft are at right angles, and are attached at one end of the imaging system by a bushing that restrains the image sensor motion. The imaging system is maintained in focus by a spring mechanism that locates the imaging system relative to the platen window. The second prior art arrangement includes a belt or pulley guide system in which the imaging system is pulled along the length of the scanner. See for example U.S. Pat. No. 4,500,197 to Dannat entitled TRANSPORT MEANS FOR FLAT BED SCANNER (issued Feb. 19, 1985) and U.S. Pat. No. 5,708,516. to Lin entitled MOVING MECHANISM OF A SCANNER (issued Jan. 13, 1998). The belts or pulleys are attached at one or both extreme lengthwise edges of the imaging system, and are, when two belts or pulleys are used, driven in unison to obtain the proper traversing motion. Many systems are further complicated by guy wire assemblies that are needed to keep the imaging system aligned and in focus during scanning.
In typical prior art scanning systems, the power requirements of the transport mechanisms is a large fraction of the total power requirements of the system. For example, when using a prior-art scanning device under computer control, the data bus connection may power the imaging electronics and possibly even the illumination optics, and an external power source may be used to power the transport mechanism. The additional power supply needed to power prior art transport mechanisms adds complexity and cost to these systems. Recently, new computer interface standards, such as the universal serial bus (USB) standard, have become available, with the capability of supplying power to a peripheral device, such as a scanner, from the computer data bus rather than from a separate power supply. It would be advantageous to have a transport that can be powered from the computer, for example, via a USB interface. The amount of power available via such a USB is limited to about 2.5 watts. Since in a typical scanner approximately 1.75 watts is used by a CIS imaging unit, only 0.75 watts available for other uses. Prior art transport mechanisms typically require much more than 0.75 watts. The additional power supply needed to power prior art transport mechanisms adds complexity and cost to these systems.
Another limitation of prior art scanners is illustrated in FIG. 14 which shows registration marks on the outer perimeter of a prior art scanner window. The correct placement of the document on the scanner is accomplished through registration marks 1401 on the scanner housing at the edge of the platen window. As scanners are capable of accepting many different document sizes, including U.S. and European standards, and orientations, the markings on the edge of the platen window can be numerous and confusing to the operator.
The prior art imaging system transport mechanisms discussed above suffer from the following limitations: 1) the transport mechanism includes many parts to enable the imaging optics to scan smoothly across the document without any unwanted motion; 2) the transport mechanisms are bulky and not very efficient, requiring larger amounts of power to drive them than would be required with efficient, lightweight transport mechanisms; 3) for computer-controlled devices, the transport mechanisms require power in excess of that available from new computer interfaces such as a USB; and 4) useful information, including but not limited to document registration markings, are not visible through the platen window where they would be most useful. Thus there is a need in the art for an imaging system transport mechanism that is both more compact and efficient, allowing for reduced consumption of electrical power by the transport mechanism, and allowing for useful information to be visible to the scanner operator through the scanner platen window.
In one aspect of this invention, the compact design of a CIS device is exploited, resulting in a more compact scanning mechanism and in lighter and smaller scanning devices. The CIS is incorporated into a drive belt attached to the length of the CIS. The CIS is forced to traverse the document by a drive mechanism that pulls the entire belt and CIS across the document while maintaining the tension necessary to keep the document in the narrow depth of focus. This mechanism provides a uniform force on the CIS, reducing the possibility of yawing motion, and keeps the document in focus through the tension on the drive belt. The combined CIS and transport mechanism power requirements can be supplied by standard computer interfaces, requiring no additional power supplies. This new mechanism also hides the internal workings of the scanner behind a drive belt that is the size of the platen window. The drive belt can either be printed to present the operator with instructions or markings to indicate document placement or with other information, or the drive belt can be left blank to present the operator with a cleaner and less cluttered scanning device.
Accordingly, an object of the invention is to reduce the size of flat-bed scanner image sensor transport mechanisms.
It is another object of this invention to produce a more compact flat-bed scanning device.
It is yet another object of this invention to produce a computer connected scanning device that could be powered entirely from standard computer-scanner interface connections.
It is another object of this invention to produce a flat-bed scanner that presents the scanner operator with information necessary to operate the scanner, the information visible through the platen window.